In recent years, the amount of information handled by computers is increasing enormously along with the advance of information society. People access such information at various stages. Display devices and printers are used as man-machine interfaces for providing people with various information such as data and images which are stored in computers. For the present, human access to the computer information has not been fulfilled yet solely with display devices, and printing paper is still in common use as an information medium. Some advantages of printing computer information on printing paper may include legibility, ease of handling, preservation of genuineness of the information, and the like. Therefore, it is conceivable that printers and display devices will be further developed as man-machine interfaces with each complementing the other.
On the other hand, environmental protection is a critical issue which must be always considered in any social activity. Since printers require printing paper as expendables, technologies for saving paper consumption have been desired. Heretofore, techniques for providing accurate print information to an operator or user before printing in order to prevent print errors, and techniques for reusing printing paper have been studied. However, ink or toner for use in printing information such as characters, figures or images is generally prepared to conserve printed conditions over the long term. Therefore, once paper is printed, it is hardly possible to reuse the paper to print new information thereon unless old information is erased in some way, otherwise the paper is mashed into pulp to fabricate new paper again.
It has been known in the art to reuse printed paper by scanning both planes of paper with a scanner and printing on a unprinted plane, or by applying erasing ink onto the entire surface of a printed plane. Further, as disclosed in Japanese Unexamined Patent Publication No. H6-286269, it is also known to use special fading ink upon printing and erase printed contents by a reaction with an erasing agent.
However, using back sides of printing paper is not sufficient to recycle paper resources, and the method of applying the erasing ink onto the entire surface of the printed plane incurs problems that ink consumption becomes large, and the paper is hardened due to the applied ink which causes inconvenience to paper handling. Also, in the method of using the special ink, the ink itself is expensive, printing paper printed by other conventional printers cannot be reused, and it is necessary to investigate whether it is effective in long term preservation. Therefore, it would be desirable to develop a printing method and apparatus to allow the reuse of printing paper while addressing the problems and shortcomings of known methods discussed above.